Intraindividual Variability and Temporal Stability of Mid-Sleep on Free and Workdays

Area of Science:

• Chronobiology
• Sleep Science
• Psychology

Background:

• Individual differences in sleep timing, known as chronotype, are often measured by mid-sleep.
• Understanding the variability and stability of chronotype is crucial for sleep research.

Purpose of the Study:

• To investigate the intraindividual variability and long-term temporal stability of mid-sleep.
• To examine the influence of age on mid-sleep stability.

Main Methods:

• Study 1: A 2-week experience sampling study with British university students.
• Study 2: A longitudinal panel study of Estonian adults using the Munich Chronotype Questionnaire, with assessments up to 5 years apart.

Main Results:

• Approximately 50% of daily mid-sleep variance was intraindividual in Study 1.
• Intraindividual variability in daily mid-sleep was smaller than interindividual variability when differentiating between free and workdays.
• Mid-sleep on free and workdays demonstrated good temporal stability over 0-5 years (retest correlations of 0.66 and 0.58, respectively).
• Mid-sleep stability increased with age, peaking in the late 40s to early 50s.

Conclusions:

• Mid-sleep exhibits considerable daily fluctuation but is temporally stable over longer periods.
• Age significantly impacts the stability of mid-sleep timing, with greater stability in middle adulthood.
• Further longitudinal research is needed to explore factors influencing mid-sleep variability and stability across the lifespan.